Metering combustion control

ABSTRACT

Metering combustion control in a fired equipment is disclosed in which both the fuel flow rate and the combustion air flow rate are metered in a desired ratio corresponding to a master firing rate demand, and the master firing rate demand combustion air flow directed to the combustion air regulating element is trimmed in response to an error based correction adjustment determined from the respective values of the fuel flow meter and combustion air flow meter input signals to drive the ratio between the fuel flow rate and the combustion air flow rate toward the desired ratio for controlling the combustion in accordance with the master firing rate demand.

FIELD OF THE INVENTION

The present invention relates generally to combustion control for use infired equipment and deals more particularly with a metering combustioncontrol for fired equipment.

BACKGROUND OF THE INVENTION

Combustion control strategies applied to fired equipment, bothcommercial and industrial, generally are one of three general categorytypes or some subtle variation to one or the other of them. The controlstrategies as known to a person skilled in the art are: 1) single pointpositioning control also known as jackshaft positioning; 2) parallelpositioning control; and 3) metered cross-limited control.

Each of these are fuel/air ratio combustion control strategies wherein afiring rate demand signal generated as a result of an attempt tomaintain a selected “process variable” (PV) equal to a desired“set-point” (SP) is simultaneously directed to a fuel flow regulatingelement and a combustion air flow regulating element.

The currently known and implemented combustion control strategies arenot entirely satisfactory. To applicant's knowledge, none of the knowncombustion control strategies meet Underwood Laboratories (UL) approvalas a parameter based combustion control instrument capable of carryingout a metering fuel/air ratio combustion control strategy.

The currently known and implemented metered cross-limited combustioncontrol strategies are not entirely satisfactory. Currentimplementations utilize two, or more, PID(Proportional-Integral-Derivative) control logic blocks, one for fueland one for air. Cross-limiting logic must be applied to coordinate thetwo independent proportional integral derivative logics. Thiscombination requires considerable skill to tune and calibrate, andresults in a slow firing rate demand response time.

Accordingly what is needed is a parameter based combustion controlinstrument capable of choosing via parameter selection a selected one ofa single point positioning control strategy, a parallel positioningcontrol strategy and a metering fuel/air ratio combustion controlstrategy.

SUMMARY OF THE INVENTION

In accordance with a broad aspect of some embodiments of the invention,combustion is controlled in a fired equipment by metering both the fuelflow rate and the combustion air flow rate in a desired ratiocorresponding to a master firing rate demand, and by trimming the masterfiring rate demand directed to the combustion air regulating element inresponse to an error based correction adjustment determined from therespective values of the fuel flow meter and combustion air flow meterinput signals to drive the ratio between the fuel flow rate and thecombustion air flow rate toward the desired ratio for controlling thecombustion in accordance with the master firing rate demand

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a function schematic representation of an example of aparallel positioning combustion control system.

FIG. 2 is a functional schematic representation of an example of aparallel positioning combustion control system with oxygen trim.

FIG. 3 is a functional schematic representation of an example of a fullmetering combustion control system with fuel flow and combustion airflow cross limiting.

FIG. 4 is a functional schematic representation of an example of ametering combustion control system with oxygen trim according to someembodiments of the present invention.

FIG. 5 shows a flowchart of the basic steps of the method according tosome embodiments of the invention.

FIG. 6 shows a combustion controller enabled device according to someembodiments of the invention for providing combustion control in a firedequipment.

FIG. 7 is a functional block diagram of an example of a signal processorfor carrying out the invention.

FIG. 8 is a functional block diagram of an example of a combustioncontroller for carrying out the steps of the method according to someembodiments of the invention.

FIG. 9 shows a combustion controller chipset according to someembodiments of the invention for providing combustion control in a firedequipment.

WRITTEN DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The basic purpose and intent of a combustion control strategy in a firedequipment is to maintain as stated above a process variable equal to adesired set-point by directing a firing rate demand signal to a fuelflow regulating element and a combustion air flow regulating element inthe fired equipment. Such fired equipment may be for example, a steamgenerator, a hot water heater, a boiler, a chemical process heater, aheated manufacturing process, or other boiler combustion fired equipmentalthough the invention is not limited to such fired equipment. Forpurposes of explanation and by way of example only, consider a steamgenerator. In this case the process variable is the steam pressure.Under the combustion control strategy, a reduction in the steam pressurerelative to the set-point of the desired pressure results in an increasein the master firing rate demand signal with a coincidental call for anincrease in the fuel input and combustion air input to the burner toincrease the firing rate to produce more steam to drive the pressureupward toward the desired pressure. Likewise, an increase in the steampressure relative to the set-point results in a decrease in the masterfiring rate demand signal with a coincidental call for a decrease in thefuel input and combustion air input to decrease the firing rate toproduce less steam to drive the pressure downward toward the desiredpressure.

For further purposes of explanation and by way of a further example,consider a hot water heater. In this case the process variable is hotwater temperature. Under the combustion control strategy, a reduction inwater temperature relative to the set-point of the desired watertemperature results in an increase in the master firing rate demandsignal with a coincidental call for an increase in the fuel input andcombustion air input to the burner to increase the firing rate toproduce hotter water to drive the water temperature upward toward thedesired water temperature. Likewise, an increase in the watertemperature relative to the set-point results in a decrease in themaster firing rate demand signal with a coincidental call for a decreasein the fuel input and combustion air input to decrease the firing rateto lessen the heat input allowing the water temperature to decrease thusdriving the water temperature toward the desired water temperature.

In both examples, a reduction in the process variable relative to theset-point results in an increase in the master firing rate demand signal(MFDS) with a coincidental call for an increase in fuel and combustionair inputs to the burner of the fired equipment while an increase in theprocess variable relative to the set-point results in a decrease in theMFDS and the fuel and combustion air inputs.

FIG. 1 shows a schematic representation of a combustion controllergenerally designated 10 in which a parallel positioning control strategyis utilized. Two firing rate demand signals are used in parallelpositioning control, with one signal going to the fuel flow regulatingelement and the other going to the combustion air regulating element,hence the term parallel positioning. For example, a reduction in theprocess variable relative to the set-point results in an increase in themaster firing rate demand signal with a coincidental call for anincrease in the fuel input and combustion air input to the firedequipment, whereas an increase in the process variable relative to theset-point results in a decrease in the master firing rate demand signaland as a result a decrease in the fuel input and the combustion airinput. As shown in FIG. 1, the master firing rate demand signals aregenerated or retrieved from a suitably configured module 10 a. Thegenerated output (0 to 100%) is the result of a comparison of the designoperating set-point versus the actual process state. The fuel firingrate demand signal is conditioned by a fuel function generator module 10b and directed to the fuel flow regulating element 10 c. The fuelfunction generator 10 b characterizes the opening of the fuel flowregulating element to produce a near linear fuel flow as a function ofthe master firing rate demand signal. The fuel flow regulating element10 c may be for example, a flow control valve or a metering pump, and isresponsive to the fuel firing rate demand signal from the fuel functiongenerator module 10 b to increase or decrease fuel flow. The combustionair firing rate demand signal is conditioned by a combustion airfunction generator 10 d and directed to the air flow regulating element10 e. The combustion air function generator 10 d characterizes theopening and/or speed of the air flow regulating element 10 e to producethe desired fuel/air ratio as a function of the master firing ratedemand signal. The fuel/air ratio is not a constant and varies due tothe need to maintain ideal fuel/air mixing velocity ratios throughoutthe burner firing rate range. The air flow regulating element 10 e maybe for example, a burner or forced draft fan damper and/or a forceddraft fan variable frequency drive or a turbine.

Another combustion control strategy known as “single point positioning”or “jackshaft positioning” control is a variation of the parallelpositioning control strategy in which the flow regulating elements areof a design that is arranged to regulate their respective flows via theaction of one or more linkage rods, each of which are connected to acommon “jackshaft”. That jackshaft is in turn mechanically linked to asingle positioning actuator or servo-motor, which receives the masterfiring rate demand signal input. In this way only one master firing ratedemand signal is directed to the fired equipment and the relative flowregulating characteristics of each flow regulating element, i.e., thefuel flow regulating element and the combustion air flow regulatingelement, is accomplished by mechanical means, for example, linkageadjustments, or adjustable cam/roller assemblies or both or in otherways well known and understood by those skilled in the art.

FIG. 2 shows a schematic representation of a combustion controllergenerally designated 12 in which a parallel positioning control strategywith oxygen trim is utilized. As explained in connection with thediscussion of FIG. 1, two firing rate demand signals are used with thefuel firing rate demand signal going to the fuel flow regulating elementand the combustion air firing rate demand signal being trimmed prior togoing to the combustion air regulating element. As shown in FIG. 2, themaster firing rate demand signals are generated or retrieved from asuitably configured module 12 a. The generated output (0 to 100%) is aresult of a comparison of the design operating set-point versus theactual process state. The fuel firing rate demand signal is conditionedby a fuel function generator module 12 b and directed to the fuel flowregulating element 12 c. The fuel function generator 12 b characterizesthe opening of the fuel flow regulating element to produce a near linearfuel flow as a function of the master firing rate demand signal. Thefuel flow regulating element 12 c may be for example, a flow controlvalve or a metering pump, and is responsive to the fuel firing ratedemand signal from the fuel function generator module 12 b to increaseor decrease fuel flow. A flue gas oxygen analyzer module 12 d determinesthe actual oxygen in the flue gas. An air demand trim computer module 12e compares the actual oxygen content in the flue gas to a master firingrate demand-based flue gas excess oxygen set-point and adjusts eitherthe master firing rate demand combustion air flow signal input to thecontroller or the master firing rate demand signal combustion air flowsignal directed to the air flow regulating element. Generally, theoxygen trim computation will include limits on the amount of variationthat can be enacted to change the master firing rate demand combustionair flow signal because of the concern for possible failure of the fluegas oxygen analyzer. The master firing rate demand combustion air flowsignal is conditioned by a combustion air function generator 12 f anddirected to the air flow regulating element 12 g. The combustion airfunction generator 12 f characterizes the opening and/or speed of theair flow regulating element 12 g to produce the desired fuel/air ratioas a function of the master firing rate demand signal. The air flowregulating element 12 g may be for example, a burner or forced draft fandamper and/or a forced draft fan variable frequency drive or a turbine.The fuel/air ratio is not a constant and varies due to the need tomaintain ideal fuel/air mixing velocity ratios throughout the burnerfiring rate range.

FIG. 3 shows a schematic representation of a combustion controllergenerally designated 14 in which a full metering control strategy withfuel flow and combustion air flow cross limiting is utilized. In atraditional full metering combustion control system, the values of therespective input of the actual fuel flow and the combustion air flow arecompared to their respective flow set-point in a proportional integralderivative controller. The actual firing rate demand signal for the fuelflow input and the combustion air flow input is then the errorcorrection based output signal from the respective controller. Theset-point of each of the fuel flow controller and the combustion airflow controller was originally the master firing rate demand signal. Thetraditional full metering control strategy differs from the ‘basic’jackshaft and parallel positioning control strategies (without oxygentrim) in that neither of those strategies has any form of “feedback”pertaining to the actual affect on flow rates resulting from a change inthe master firing rate demand signal. The addition of “cross limiting”adds low and high signal selectors and logic to assure that on increasesin the firing rate, the air demand would increase before the fuel demandand on decreases in firing rate, the reverse action would be assured.

Still referring to FIG. 3, the master firing rate demand signals aregenerated or retrieved from a suitably configured module 14 a. Thegenerated output (0 to 100%) is a result of a comparison of the designoperating set-point versus the actual process state. The fuel flowmaster firing rate demand signal is input to a low value selector module14 d along with an actual combustion air flow signal from a combustionair flow transmitter module 14 e to provide a fuel set-point signal thatis input to the fuel flow proportional integral derivative controller 14c along with an actual value of the fuel flow signal from a fuel flowtransmitter module 14 b to provide a fuel firing rate demand signal. Thefuel firing rate demand signal is conditioned by a fuel functiongenerator module 14 f and is directed to the fuel flow regulatingelement 14 g. The fuel function generator 14 f characterizes the openingof the fuel flow regulating element to produce a near linear fuel flowas a function of the master firing rate demand signal. The fuel flowregulating element 14 g may be for example, a flow control valve or ametering pump, and is responsive to the fuel firing rate demand signalfrom the fuel function generator module 14 f to increase or decreasefuel flow. The combustion air flow master firing rate demand signal isinput to a high value selector module 14 h along with an actual fuelflow signal from the fuel flow transmitter module 14 b to provide an airflow set-point that is input to the air flow proportional integralderivative controller 14 i along with an actual combustion air flowsignal from the combustion air flow transmitter module 14 e to provide acombustion air firing rate demand signal. The combustion air firing ratedemand signal is conditioned by a combustion air function generator 14 jand directed to the air flow regulating element 14 k. The combustion airfunction generator 14 j characterizes the opening and/or speed of theair flow regulating element 14 k to produce the desired fuel/air ratioas a function of the master firing rate demand signal. The air flowregulating element 14 k may be for example, a burner or forced draft fandamper and/or a forced draft fan variable frequency drive or a turbine.The fuel/air ratio is not a constant and varies due to the need tomaintain ideal fuel/air mixing velocity ratios throughout the burnerfiring rate range.

Turning now to FIG. 4, a functional schematic representation of anexample of a metering combustion control system with oxygen trimaccording to some embodiments of the present invention is shown thereinand generally designated 16. Now in contrast to the combustion controlsystem strategies discussed above, the metering combustion controlsystem strategy with oxygen trim embodying the present invention blendsthe benefits of all of the above described approaches by using therespective flow meter input signals in combination with the masterfiring rate demand signals in a proportional integral controller to“trim” the basic parallel positioning master firing rate demand signalbeing directed to the air flow regulating element. Further, limits areapplied to the allowable level of error correction based adjustment sothat even if there is a flow meter failure, continued operation in thebasic parallel positioning format (with or without oxygen trim) ispossible. Ideally the fuel input varies linearly with the master firingrate demand whereas for reasons associated with maintaining optimummixing influenced velocities, the combustion air level is relativelyhigher at lower firing rates (i.e. fuel/air ratio is not a constantthroughout the range).

As shown in FIG. 4, the master firing rate demand signals are generatedor retrieved from a suitably configured module 16 a. The generatedoutput (0 to 100%) is a result of a comparison of the design operatingset-point versus the actual process state. The firing rate demand signalis applied simultaneously to a fuel function generator 16 b and an airflow demand summing module 16 k. The fuel function generator 16 bcharacterizes the opening of the fuel flow regulating element 16 c toproduce a near linear fuel flow as a function of the master firing ratedemand signal. The air flow demand summing module 16 k adds the firingrate demand signal to the air flow proportional integral derivativecontroller 16 g trim signal and applies the resultant signal to thecombustion air function generator 16 i. The combustion air functiongenerator 16 i characterizes the opening and/or speed of the air flowregulating element 16 j to produce the desired fuel/air ratio as afunction of the master firing rate demand signal. The fuel/air ratio isnot a constant and varies due to the need to maintain ideal fuel/airmixing velocity ratios throughout the burner firing rate range.

The fuel flow regulating element 16 c may be for example, a flow controlvalve or a metering pump, and is responsive to the fuel firing ratedemand signal from the fuel function generator module 16 b to increaseor decrease fuel flow. The air flow regulating element 16 j may be forexample, a burner or forced draft fan damper and/or a forced draft fanvariable frequency drive or a turbine.

A flue gas oxygen analyzer module 16 d determines the actual oxygen inthe flue gas. An air flow trim computer module 16 e receives a signalrepresentative of the value of the actual oxygen in the flue gas alongwith a signal representative of the combustion air flow from acombustion air flow transmitter module 16 f to provide an adjustedcombustion air flow signal in accordance with the required oxygencontent in the flue gas. The output signal from the air flow trimcomputer module 16 e is input to an air flow proportional integralderivative controller module 16 g along with the value of the actualfuel flow from a fuel flow transmitter module 16 h for determining thecombustion air flow trim signal to be directed to the air flow demandsumming module 16 k.

It should be recognized that the turndown capability (i.e. ability tooperate at reduced rates) of a burner governed by a traditional meteringcontrol strategy is tied to the flow meter's limited turndowncapabilities that is, flow measurement accuracy at reduced rates. Incontrast according to some embodiments of the present invention, theturndown capabilities are equivalent to that of parallel positioning dueto the lack of the absolute dependence on the fuel flow and combustionair flow signals.

It should be recognized that according to some embodiments of thepresent invention, the fuel and air regulating elements (16 c and 16 j)respond instantly to changes in the firing rate demand 16 a. Incontrast, traditional metered control strategy low selector 14 d, highselector 14 h and the differing response rates of fuel proportionalintegral derivative controller 14 c and air flow proportional integralderivative controller 14 i all combine to delay the response of therespective fuel and air regulating elements (16 c and 16 j) to a changein the firing rate demand 16 a.

FIG. 5 shows a flowchart of the basic steps of the method for meteringcombustion control in fired equipment according to some embodiments ofthe present invention. The basic method is shown in the flowchartgenerally designated 20 and includes the steps of controlling combustionin a fired equipment, for example a steam boiler or hot water heater bymetering both the fuel flow rate and the combustion air flow rate in adesired ratio corresponding to a master firing rate demand (step 20 a),and trimming the master firing rate demand signal directed to thecombustion air regulating element in response to an error basedcorrection adjustment determined from the respective values of the fuelflow meter and combustion air flow meter input signals to drive theratio between the fuel flow rate and the combustion air flow rate towardthe desired ratio for controlling the combustion in accordance with themaster firing rate demand (step 20 b).

FIG. 6 shows by way of example a metering combustion control enableddevice 22 according to some embodiments of the invention for use in afired equipment 24 such as described above. The metering combustioncontrol enabled device 22 includes one or more modules 22 a configuredfor controlling combustion in a fired equipment, for example a boiler orhot water heater, according to a master firing rate demand, one or moremodules 22 b configured for metering the fuel flow rate and thecombustion air flow rate in a desired ratio to correspond to the masterfiring rate demand, one or more modules 22 c configured for providing anerror based correction adjustment based on the value of the fuel flowmeter input signal and the value of the combustion air flow meter inputsignal, and one or more modules 22 d configured for trimming the masterfiring rate demand signal value directed to the combustion air flowregulating element in response to the error based correction adjustmentto drive the ratio between the fuel flow rate and the combustion airflow rate toward the desired ratio for controlling the combustion inaccordance with the master firing rate demand. Consistent with thatdescribed above, the metering combustion control enabled device mayinclude other modules 22 e that do not necessarily form part of theunderlying invention and are not described in detail herein.

By way of example, and consistent with that described above, thefunctionality of the modules 22, 22 a, 22 b 22 c, 22 d and/or 22 e maybe implemented using hardware, software, firmware, or a combinationthereof, although the scope of the invention is not intended to belimited to any particular embodiment thereof. In a typical softwareimplementation, the modules 22 a, 22 b, 22 c and 22 d would be one ormore microprocessors-based architectures having a microprocessor, arandom access memory (RAM), a read only memory (ROM), input/outputdevices, memory, flow meter control, and control, data and address busesconnecting the same such as shown in FIG. 7. A person skilled in the artwould be able to program such a microprocessor-based implementation toperform the functionality described herein without undueexperimentation. The scope of the invention is not intended to belimited to any particular implementation using technology now known orlater developed in the future. Moreover, the scope of the invention isintended to include the modules 22 a, 22 b, 22 c and 22 d being astandalone module, as shown, or in the combination with other circuitryfor implementing another module. Moreover, the real-time part may beimplemented in hardware, while the non-real-time part may be done insoftware.

According to some embodiments the present invention may be implementedas a computer program product comprising a computer readable structureembodying computer program code therein for execution by a computerprocessor instructions for performing a method comprising controllingcombustion in a fired equipment according to a master firing ratedemand; metering the fuel flow rate and the combustion air flow rate ina desired ratio to correspond to the master firing rate demand;providing an error based correction adjustment based on the value of thefuel flow meter input signal and the value of the combustion air flowmeter input signal, and trimming the master firing rate demand signalvalue directed to the combustion air flow regulating element in responseto the error based correction adjustment to drive the ratio between thefuel flow rate and the combustion air flow rate toward the desired ratiofor controlling the combustion in accordance with the master firing ratedemand.

Turning now to FIG. 8, a schematic functional block diagram of anexample of a metering combustion control is illustrated therein showingthe major operational functional components which may be required tocarry out the intended functions of the combustion controller andimplement the steps of the method according to some embodiments of theinvention and is generally designated 24. A processor such as the signalprocessor of FIG. 7 carries out the computational and operationalcontrol of the metering combustion control in accordance with one ormore sets of instructions stored in a memory. A user interface may beused to provide alphanumeric input and control signals or other programsteps and set-points by a user and is configured in accordance with theintended function to be carried out. A display sends and receivessignals from the controller that controls the graphic and textrepresentations shown on a screen of the display in accordance with thefunction being carried out. The controller controls a fuel flow meterand an air combustion flow meter that operate in a manner well known tothose skilled in the art. The functional logical elements for carryingout the metering combustion control operational functions are suitablyinterconnected with the controller to carry out the metering combustioncontrol as contemplated in accordance with some embodiments of theinvention. An electrical power source such as a battery is suitablyinterconnected within the combustion controller to carry out thefunctions described above. It will be recognized by those skilled in theart that the metering combustion control according to some embodimentsof the invention may be implemented in other ways other than that shownand described, including using pneumatic control elements and othermechanical and electrical devices. It will also be recognized by thoseskilled in the art that the metering combustion control strategy forfired equipment according to some embodiments of the invention can beimplemented using other suitably configured and arranged devicesincluding but not limited to pneumatic, electronic, microprocessor,computer, signal processor, logic devices, wired logic, firmware,computational and memory components, software instruction sets, andother devices and components now known or future developed.

Consistent with that discussed above, the metering combustion controlaccording to some embodiments of the invention may be implemented as achipset for use in a combustion control enabled fired equipmentgenerally designated 26 for example as illustrated in FIG. 9. Themetering combustion control chipset generally designated 26 a issuitably configured for controlling combustion in a fired equipment bymetering both the fuel flow rate and the combustion air flow rate in adesired ratio corresponding to a master firing rate demand, and fortrimming the master firing rate demand directed to the combustion airregulating element in response to an error based correction adjustmentdetermined from the respective values of the fuel flow meter andcombustion air flow meter input signals to drive the ratio between thefuel flow rate and the combustion air flow rate toward the desired ratiofor controlling the combustion in accordance with the master firing ratedemand. Consistent with that described above, the metering combustioncontrol chipset may include other metering combustion chipsets 26 b thatdo not necessarily form part of the underlying invention and are notdescribed in detail herein.

1. Method, comprising: controlling combustion in a fired equipmentaccording to a master firing rate demand; metering the fuel flow rateand the combustion air flow rate in a desired ratio to correspond to themaster firing rate demand; providing an error based correctionadjustment based on the value of the fuel flow meter input signal andthe value of the combustion air flow meter input signal, and trimmingthe master firing rate demand signal value directed to the combustionair flow regulating element in response to the error based correctionadjustment to drive the ratio between the fuel flow rate and thecombustion air flow rate toward the desired ratio for controlling thecombustion in accordance with the master firing rate demand.
 2. Themethod according to claim 1 further comprising the fuel flow inputsignal and the combustion air flow input signal being input to aproportional integral derivative controller for determining the value ofthe error based correction adjustment.
 3. The method according to claim1 further comprising limiting in response to the failure of a fuel flowmeter and/or an air combustion flow meter, the value of the errorcorrection based adjustment to a predetermined allowable level to insurecontinued combustion.
 4. The method according to claim 1 furthercomprising providing a turndown capability without dependence on flowmeter flow signals.
 5. The method according to claim 4 wherein theturndown capability is equivalent to a parallel positioning combustioncontrol operation.
 6. The method according to claim 1 further comprisingproviding a reduced response time capability without dependence on lowselectors, high selectors or differences in independent fuel and airflow PID tunings.
 7. The method according to claim 1 further comprisingcontrolling the fuel British Thermal Unit (BTU) flow rate andcontrolling the combustion air oxygen mass flow rate.
 8. The methodaccording to claim 1 further comprising analyzing the oxygen level inthe flue gas for adjusting the combustion air flow meter input signal.9. The method according to claim 1 further comprising characterizing theopening of the fuel flow regulating element to produce a near linearfuel flow as a function of the trimmed master firing rate demand signaldirected to the fuel flow regulating element.
 10. The method accordingto claim 1 further comprising characterizing the opening/speed of theair flow regulating element to produce the desired fuel flowrate/combustion air flow rate ratio as a function of the trimmed masterfiring rate demand signal directed to the combustion air flow regulatingelement.
 11. A controller, comprising: one or more modules configuredfor controlling combustion in a fired equipment according to a masterfiring rate demand; one or more modules configured for metering the fuelflow rate and the combustion air flow rate in a desired ratio tocorrespond to the master firing rate demand; one or more modulesconfigured for providing an error based correction adjustment based onthe value of the fuel flow meter input signal and the value of thecombustion air flow meter input signal, and one or more modulesconfigured for trimming the master firing rate demand signal valuedirected to the combustion air flow regulating element in response tothe error based correction adjustment to drive the ratio between thefuel flow rate and the combustion air flow rate toward the desired ratiofor controlling the combustion in accordance with the master firing ratedemand.
 12. The controller according to claim 11 further comprising oneor more modules configured as a proportional integral derivativecontroller for determining the value of the error based correctionadjustment based on the respective values of the fuel flow input signaland the combustion air flow input signal.
 13. The controller accordingto claim 11 wherein said fired equipment is a boiler configured andarranged for generating steam.
 14. The controller according to claim 11wherein said fired equipment is a hot water heater.
 15. The controlleraccording to claim 11 wherein said fired equipment is at least one of asteam generator, a boiler, a chemical process heater, a heatedmanufacturing process, a boiler combustion fired equipment.
 16. Acomputer program product comprising a computer readable structureembodying computer program code therein for execution by a computerprocessor, said computer program further comprising instructions forperforming a method comprising controlling combustion in a firedequipment according to a master firing rate demand; metering the fuelflow rate and the combustion air flow rate in a desired ratio tocorrespond to the master firing rate demand; providing an error basedcorrection adjustment based on the value of the fuel flow meter inputsignal and the value of the combustion air flow meter input signal, andtrimming the master firing rate demand signal value directed to thecombustion air flow regulating element in response to the error basedcorrection adjustment to drive the ratio between the fuel flow rate andthe combustion air flow rate toward the desired ratio for controllingthe combustion in accordance with the master firing rate demand.
 17. Amethod according to claim 1 wherein the method further comprisesimplementing the steps of the method via a computer program running in aprocessor, controller or other suitable module located in or interfacedwith the fired equipment.
 18. A chipset, comprising: a first chipsetmodule configured for controlling combustion in a fired equipment bymetering both the fuel flow rate and the combustion air flow rate in adesired ratio corresponding to a master firing rate demand, and a secondchipset module configured for trimming the master firing rate demanddirected to the combustion air regulating element in response to anerror based correction adjustment determined from the respective valuesof the fuel flow meter and combustion air flow meter input signals todrive the ratio between the fuel flow rate and the combustion air flowrate toward the desired ratio for controlling the combustion inaccordance with the master firing rate demand.
 19. The chipset accordingto claim 18 further comprising a proportional integral derivativecontroller configured for determining the value of the error basedcorrection adjustment based on the respective values of the fuel flowinput signal and the combustion air flow input signal.